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on computer motherboards - why are some socket surface mount while others are not?

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Michael

Jan 1, 1970
0
Hi - I was just looking at a motherboard - and I noticed that the PCI and
DIMM slots all used through hole mounting (I think that's what it's called?
Where pins stick through the board) while the CPU socket was surface mount.
What's the advantage to using surface mount in such a situation instead of
through hole mounting? My guess was that using a surface mount socket
allowed traces to go directly under the socket in some of the middle
layers. But really I just don't know... Any ideas? Thanks,

Michael
 
J

James Meyer

Jan 1, 1970
0
Hi - I was just looking at a motherboard - and I noticed that the PCI and
DIMM slots all used through hole mounting (I think that's what it's called?
Where pins stick through the board) while the CPU socket was surface mount.
What's the advantage to using surface mount in such a situation instead of
through hole mounting? My guess was that using a surface mount socket
allowed traces to go directly under the socket in some of the middle
layers. But really I just don't know... Any ideas? Thanks,

Michael

I think you're right about the CPU socket.

The DIMM and PCI sockets are most likely through-hole because the stuff
that will be plugged into them will need some fair amount of mechanical force
from time to time and surface mounted sockets are more fragile.

Jim
 
M

Mac

Jan 1, 1970
0
I think you're right about the CPU socket.

The DIMM and PCI sockets are most likely through-hole because the stuff
that will be plugged into them will need some fair amount of mechanical force
from time to time and surface mounted sockets are more fragile.

Jim

Yeah. It's the two things. You can route under surface mount connectors,
and when you have a high density of signals, as near a CPU, the extra
routing space is very helpful.

The through-hole connectors are mechanically much stronger because they
are soldered on the back side of the board. The surface mount connectors
stick really well to their copper pads, but the adhesion between the pads
and the fiberglass isn't nearly as good as the positive mechanical
attachment of the through-hole parts. So, you might be able to lift a
surface-mount connector if you pull hard enough.

Mac
 
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